Atoms are the smallest particles that make up all matter.  Each element has a different kind of atom.

Atomic Theory says:

All matter is made of atoms.

Each element has its own kind of atom.

There are about 100 kinds of atoms.

Most substances are compounds and made of more than one kind of atom.

The Nucleus is the center , heavy part of an atom. The nucleus is made up of protons and neutrons.

A Proton is a part of an atom found in the nucleus and it has a positive charge and an atomic weight of one atomic mass unit.

A Neutron is a part of an atom found in the nucleus and has no charge and an atomic weight of one atomic mass unit.

An Electron is an atom part found outside the nucleus in electron shells. They have a negitive charge and an atomic weight of zero atomic mass units, because they are so small compared to protons or neutrons.

Electron Shells are layers outside the nucleus where the electrons are. Each shell is a different energy level.

The Valence Shell is the outermost electron shell that an atom has and if it is not full that atom can bond to other atoms.

An Element is a substance composed of one kind of atom.

A Symbol is sign that stands for an object . Chemical symbols are letters that represent a a kind of atom.

 The Periodic Table of Elements is a chart listing all of the kinds of atoms or elements in the universe according to their properties.

 Dmitri Mendeleev arranged elements in groups and invented the periodic table.  

The Atomic Number of an atom is the protons in an atom. The Periodic Table of Elements is arranged from lowest atomic number at the top to highest at the bottom.

Atomic Mass (Weight) is the total number of protons PLUS neutrons in the nucleus of an atom.

Groups are columns on the periodic table. A group contains elements that are similar physically and in how they react with other atoms.

Periods are rows on the periodic table. The row number tells how many electron shells the atom has. All the elements in a period have the same number of electron shells.

Metals are shiny solid substances (except mercury) that are good conductors of heat & electricity, they are malleable (they bend) and ductile (they can be pulled into a wire).

Most Non-Metals are solid or gas (except bromine which is a liquid). They are insulators and are brittle if solid.

The Noble Gases are a periodic table group of gases that don’t ever react with other atoms because their valence shell is full.

Compounds are substances with 2 or more kinds of atoms that are bonded together in a definite ratio. The atoms bond together to fill their outside, valence shell .

A Molecule is a particle of matter made of more than one atom (can be the same kind). It is the smallest particle of a compound.

A Formula is a symbol combination that represents a molecule of a compound.

Bonds are connections between atoms that store energy and hold the atoms together to make a molecule that is more stable.

Subscripts are small numbers to the right and below an element symbol in a formula. It tells how many of that kind of atoms are in a molecule of that substance.

Coefficient is a number in front of an element symbol or formula that tells how many molecules participate in a chemical reaction.

A Mixture is 2 or more kinds of atoms mixed together but not bonded together. Mixtures can be separated or unmixed to recover the components.

A Solution is a mixture where a material is dissolved in a liquid. The solute atoms spread out and fit in between the solvent atoms.

A Solvent is the liquid that dissolves another material. Water is called the universal solvent, because many materials can dissolve into it.

A Solute can be a solid, liquid or gas and dissolves into a liquid to form a solution.

Solubility is the ability of a material to dissolve or how much can dissolve.

Concentration is how much of material is dissolved into a solution.